I always liked the way Objective-C added the message passing syntax in a way which fit in well with C. The [squareBrackets means: "we're in SmallTalk land"] looks nice to me. The @ (at sign) sigils I don't appreciate as much.

> I think it could be improved by having the Smalltalk-side be the default

It does kind of seem like you'd want the higher level language on the outside and only dive into the lower language when you need it, but I could go either way for that.